At present, more than 40 counties in the world have opened urban subway lines, and developed counties own highly developed urban subway facilities. Subways have borne a main passenger transportation task in traffic of many cities, and the lives of residents in such cities as Moscow, New York, Beijing and the like is inseparable from the subways. Due to the advantages and convenience of rail transit, more and more countries and cities begin to develop their rail transit. With the rapid development of worldwide rail transit, more and more tunnels will be built in each country in the field of rail transit. Compared with traditional tunnel construction methods such as an open cut method, shallow-buried tunneling method and the like, the shield construction method has the advantages of “high tunneling speed, high production efficiency, civilized construction environment, good technical and economic superiorities” and the like, so increasing international subway tunnels are built by adopting the shield construction method at present, wherein the earth pressure balance shield is a common shield form in the shield construction.
The earth pressure balance shield construction belongs to full-section tunnel boring machine construction and is mainly used for urban underground soft soil ground layer construction, and the bad geological condition is more complex due to shallow burying and abrupt changes of geological units. Meanwhile, since urban ground buildings are dense, it is difficult to comprehensively find out the bad geological condition along the subway line by ground investigation. Once bad geological bodies such as water rich quick sand layers, water-containing corrosion cavities, boulders and the like are encountered in the excavation process, and engineering accidents such as collapse, water outburst, ground surface settlement and the like often happen, situations are caused ranging from damage of shied machinery and construction period delay to stratum collapse resulting in major safety accidents. Construction disasters can be effectively avoided by detecting the information such as the position and the scale of a bad geological body and the like in advance. Accordingly, it is very necessary to carry an advanced prediction system and develop whole-course real-time advanced detection in the earth pressure balance shield. However, the whole space of a shield construction tunnel is occupied by a huge shield tunneling machine, no detection space is available for geophysical detection, meanwhile, the construction vibration of shield machinery, huge metal bodies, supporting mechanical and electrical equipment and the like seriously interfere with geophysical fields such as an electric field, a wave field and the like, as a result, common geophysical prospecting methods such as a seismic wave method, an electromagnetic method and the like for a drilling and blasting method are inapplicable. The frequency-domain electrical method is sensitive to water in response, and the focusing electrical method has the characteristic of shielding rear interference and is advantageous in the complex environment of the shield construction tunnel. The BEAM (Bore-Tunneling Electrical Ahead Monitoring) method is a tunnel boring machine advanced detection technology developed by Germany and realizes real-time detection using a shield and a cutter as a power supply electrode and a measuring electrode, but the cutter selected as an electrode on a cutter head is in contact conduction with a tunnel face, resulting in high ground resistance. Meanwhile, positioning of BEAM excessively depends on experience, so that the positioning precision is low and three-dimensional imaging cannot be realized.
Thus, carrying an electrical prospecting device on the shield tunneling machine still faces many problems, and the main problems are as follows:
(1) An earth pressure balance shield cutter head closely clings to the earth of the tunnel face all the time and cannot be retracted in order to keep the earth pressure balance of the tunnel face in the construction environment of the shield tunneling machine, so no detection space is available in front of the cutter head, and an observation mode or method available in front of the shield cutter head is the first problem to be solved.
(2) Common electrical detection adopts contact electrodes in contact coupling with the tunnel face. The electrodes and the propulsion device exposed in front of the cutter head are easily influenced by the tunneling construction and easily damaged, and it is difficult for the contact electrodes to work under the rotation of the cutter head, so how to adopt the noncontact electrodes to realize real-time advanced detection in the rotating mode of the cutter head is an important problem. In addition, the problem about a rotary junction device and an electrode positioning device also needs to be solved in order to realize real-time detection of the shield.
(3) Since noncontact electrodes are adopted, current emission and reception instruments required for frequency-domain electrical detection also need to be developed, meanwhile, in order to meet the requirement for quick construction of the shield, how to realize real-time automatic detection of a detection system is a further problem, and a system for controlling current emission, signal acquisition, electrode positioning and quick interpretation is needed.